Let’s briefly introduce these:
PLC expansion interface and PLC communication interface

(1) PLC communication interface

The PLC is equipped with a variety of communication interfaces, through which the PLC can communicate with programmers, printers, other PLCs, computers and other devices. It can be combined into a multi-machine system or connected to a network for greater control.
GCAN-PLC-400 have CAN, Ethernet, Serial communication interface, Click here to learn more about GCAN PLC.
 (2) expansion interface
Used to connect I/O expansion units and special function units. The expansion interface can expand the number of I/O points and increase the analog I/O terminals. It can also be equipped with intelligent units to perform specific functions, making the PLC configuration more flexible to meet the needs of different control systems. The I/0 expansion interface circuit adopts two circuit forms: a parallel interface and a serial interface.
In industrial control, in addition to digital signal control, sometimes analog signals are used for control. There are three types of analog modules: analog input modules, analog output modules, and analog input/output modules.
(I) Analog input module
The analog input module, also known as the A/D module, converts the continuous analog signal generated by the sensor detection into the digital quantity that the CPU of the PLC can receive. Generally, it is mostly a 12-bit binary number. The more the digital quantity, the more digits. Module, the higher the resolution.
(II) Analog output module
The analog output module, also known as the D/A module, converts the digital quantity sent by the PLC’s CPU to the analog output module into an analog quantity (voltage or current) that the external device can receive. The digital signals received by the analog output module are generally 12-bit binary numbers. The higher the number of digital bits, the higher the resolution.
More Information and Technology datasheet.